This invention relates to water treatment.
The pollution of water is a major problem around the world. The treatment of polluted water to render it potable or better able to be used in agriculture presents a major challenge.
Water is polluted in many ways. The mining industry is responsible for significant pollution of water which must be treated before it is discharged into the river systems. One of the ways water is polluted is as a result of water seeping into old, disused mine shafts. On passage through the rock, the water dissolves sulphides present in the rock producing sulphuric acid. The water which seeps into the old, disused mine shafts contains sulphuric acid and dissolved salts and can have a pH as low as 3. The mine shafts fill with the acidic water. Underground water sources are polluted with this acidic water. The shafts eventually fill with this acidic water and then the water overflows into the above-ground water ways causing serious problems. This acidic water is known as acid mine drainage (AMD), an acidic effluent of the mining industry.
AMD can be treated by reverse osmosis. Although reverse osmosis provides a very pure water product, it also produces a brine which is waste product containing significant amounts of dissolved salts of cations such as sodium, potassium, calcium, magnesium and the like salts. The brine needs to be disposed of.
Pollution of water is not only caused by human activity. Water which falls on the mountains of South Africa is pure. However, on passage down to the coast the water contacts rock and other formations and some of the minerals contained in these formations dissolves in the water. Thus, some of the water in South African rivers contain significant quantities of dissolved salts. An example of this is the water in the Sundays river. This water contains significant quantities of dissolved sodium, chloride and sulphate ions. The Sundays river water is used to irrigate crops such as citrus orchard. The dissolved ions in the water have the effect of reducing the yields obtainable from citrus trees.